The curing of monomeric materials to produce polymeric thermoset resins is well known in the art. In general, the polymerizable monomers have at least one and customarily more than one reactive group which serves as an active site for a curing or crosslinking polymerization to produce the thermoset resins. However, crosslinking of many or most polymerizable monomers, for example the curing of epoxy resins, requires the use of a curing agent, catalytic or stoichiometric, to cause the curing or crosslinking to occur at an acceptable rate. Even in the presence of most curing agents the rate of crosslinking is slower than desired and the addition of an accelerator is required to obtain sufficiently rapid curing. Some monomers will cure at an acceptable rate in the absence of curing agent but only upon application of high intensity energy, e.g., UV light.
There are other monomers wherein the active site is such that no additional curing agent or high intensity energy is necessary and the monomers will cure upon application of heat. Such monomers are termed "self-curing". One class of such monomers includes within the molecular structure moieties of an arylcyclobutene, for example, a benzocyclobutene. Without wishing to be bound by any particular theory, it appears likely that upon application of heat the cyclobutene ring undergoes ring-opening to produce active intermediates which crosslink by undergoing reaction with adjacent molecules. The resulting resins have properties of rigidity and strength.
A series of U.S. patents to Krichhoff, illustrated by U.S. Pat. No. 4,540,763, describes the production and curing of a large number of benzocyclobutene derivatives including ethers of di(hydroxyphenyl) compounds such as di(hydroxyphenyl)alkanes or bisphenol alkanes, wherein the ether oxygen directly links the phenyl ring of the di(hydoxyphenyl) compound to the six-membered ring of the benzocyclobutene group. Such monomers are said to be self-curing. The benzocyclobutene derivatives of Krichhoff are characterized by this direct link of a functional group between the benzocyclobutene moiety and the rest of the molecule.
A copending U.S. patent application, Ser. No. 349,547, filed May 9, 1989, relates to certain arylcyclobutene ester derivatives of polymeric materials wherein the carboxy function is connected to the arylcyclobutene moiety through an alkylene group. It would be of advantage to provide arylcyclobutene derivatives of di(hydroxyphenyl) compounds where the ether oxygen is connected to the arylcyclobutene moiety through an alkylene group. Such self-curing monomers crosslink upon application of heat to produce hard resins having good properties.